NRC Seeks Comments on Revised Dose Limits to Lens of the Eye

The agency says the international radiation protection community may follow the International Commission on Radiological Protection’s recommended limit of of 20 mSv (2 rem) per year, versus the current U.S. limit of 150 mSv (15 rem) per year.

Sep 01, 2011The Nuclear Regulatory Commission has asked for comments from stakeholders about possibly lowering the current U.S. occupational exposure limit for radiation to the lens of the eye. NRC hasn’t begun rulemaking on the issue, but its notices said the international radiation protection community may follow the International Commission on Radiological Protection’s recent recommended limit of of 20 mSv (2 rem) per year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv (5 rem). The current U.S. limit is seven times higher: 150 mSv (15 rem) per year.

“In particular, the International Atomic Energy Agency has specifically considered and is now incorporating, the new limits into the revision of the International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources,” NRC’s notice stated.

Protecting the eyes against the effects of ionizing radiation is designed primarily to prevent the formation of cataracts, and the sensitive part of the eye for this health effect is the lens. it noted. The radiation dose to the eye is defined by 10 CFR 20.1003 as the lens dose equivalent (LDE) at a tissue depth of 0.3 centimeters. Cataract formation falls under the class of radiation effects referred to as deterministic (tissue reactions, in current ICRP terminology). “At doses above the threshold, the severity of cataract formation increases with dose, but the radiation-induced incidence below the threshold dose is believed to be essentially zero. Currently, 10 CFR part 20 limits annual occupational exposures to the lens of the eye to 150 mSv (15 rem) per year (10 CFR 20.1201),” the notice said.

NRC asked for comments on the ICRP recommendations by Oct. 31. The commission said it seeks early input before making any decision about whether to consider this issue for future rulemaking.